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CHEMICAL CONVERSION COAT, Grade B?




2006

I am revising a legacy drawing that has a note to chemical conversion coat (Alodine) per MIL-C-5541, grade B. I am unable to find a reference to grade B. Do I need to be concerned about this? Should I also include the class 1A or 3?

Thanks,

Jeff Seufzer
Manufacturing Engineer

JEFFREY ALAN SEUFZER
ESSEX INDUSTRIES - ST. LOUIS, Missouri



2006

For proper coating selection and specifying, see MIL-DTL-5541 [on DLA]F. If doing the coating, use appropriate products from QPL-81706. Type II (non-hexavalent chromium) coatings can now be specified (although a QPL update seems significantly delayed).

In MIL-C-5541A (1964), Grade B indicates brush-on application, now Method B. Is this appropriate for the part (specifying a Method will disallow other Methods)?
QPL-5541-25 (1968, 1969 & 1970) shows that Grade B products were available for Classes 1, 2 and 3, so no clue there. Also, Alodine® is a brand name, not a specification, with many versions (the original Alodine introduced in 1945 produced a greenish phosphate-chromate coating).

For the original MIL-C-5541 (1950), I have very limited info. Most early products were phosphate-type. Requirements were 168 hours salt spray resistance (500 hours painted), and products were qualified per application method (spray, brush and immersion) -- perhaps the 'Grade.' Apparently, no separate Classes or Types. From US Navy lab testing reported by Sara J. Ketcham in The Finishing of Aluminum, G. H. Kissin, editor, (1963), the MIL-C-5541A revision added Class 3 for low electrical resistance, and (I surmise) the thickest coatings were designated Class 1 (for max. corrosion resistance when unpainted) and an intermediate thickness Class 2 was created for better paint adhesion.
Classes 1 and 2 were superseded by Class 1A in 1970 -- see Paragraph 6.3.1 of MIL-C-81706.
The MIL-C-5541A classes correspond roughly to Classes 1, 2 and 3 still present in ASTM B449.

MIL-C-81706 and QPL-5541-25 are still available from ASSIST, as are current 5541 & 81706 specs.

Ken Vlach [deceased]
- Goleta, California

contributor of the year Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.





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